[lworld] RFR: 8378368: [lworld] Add guarantees for invariants in code

[Coleen Phillimore]

Please review this simple change to add guarantees of non-null pointers in code for two places that are not possible to have null pointers.
Tested with tier1 locally, tier1-3.

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Commit messages:
 - Fix variable name and comments.
 - 8378368: [lworld] Add guarantees for invariants in code

Changes: https://git.openjdk.org/valhalla/pull/2149/files
  Webrev: https://webrevs.openjdk.org/?repo=valhalla&pr=2149&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8378368
  Stats: 9 lines in 2 files changed: 2 ins; 0 del; 7 mod
  Patch: https://git.openjdk.org/valhalla/pull/2149.diff
  Fetch: git fetch https://git.openjdk.org/valhalla.git pull/2149/head:pull/2149

PR: https://git.openjdk.org/valhalla/pull/2149